Existing systems and methods for gas turbine startup control are based on defined schedules related to various startup parameters such as, for example, minimum/maximum fuel flow, acceleration rate, starting torque, and other suitable parameters. The predefined schedules define startup characteristics for the gas turbine. Startup parameters are controlled to follow nominal paths set forth in the schedules. However, in practice, the gas turbine startup can deviate from the nominal paths set forth in the schedules due to variations in for example, ambient temperature or component performance. These deviations may not be corrected during startup and can result in significant variation in startup time for the gas turbine. This in turn can impact component life, blade tip clearances, and performance of the gas turbine.
One approach to addressing variations in startup is to allow for large margins in the startup time. However, such an approach may not always be desirable due to predictability and efficiency concerns. Moreover, guarantees of startup times for gas turbines are becoming more common commercial requirements.
Another approach that can be used to address variations in gas turbine startup is the application of a target tracking schedule. In this approach, gas turbine speed or other suitable startup parameter is monitored versus time. The control routine determines if there are any errors in gas turbine speed or other suitable parameter and controls various effectors, such as fuel flow and starting torque, to correct any errors.
However, given that gas turbine speed is a slow responding characteristic, once an error has developed, the controls may quickly saturate against established limits in an attempt to close the error. Sustained operation at control limits, such as for example, at a maximum firing or exhaust temperature, is typically not desirable. Additionally, when the error is close to zero, the lack of sensitivity can result in control loops moving quickly from one boundary to the other, creating wear and other hardware issues.
Thus, an improved gas turbine startup control system and method that provides for guaranteed startup times with reduced margins that overcome the above-mentioned disadvantages would be welcome in the art.